Furnace damper and fuel control system



N. F. HAHN ET AL Filed July l5, 1953 FURNACE DAMPER AND FUEL CONTROL SYSTEM Aug. 27, 1957 INVENTOR. NORMAN F- HAHN 'ARTHUR A. KRAFT BY 'men ATT Y.'

United States Patent O FURNACE DAMPER ANDFUE'L CONTROL SYSTEMV Norman F. Hahn, Parma;I and Arthur A. Kraft, Cleveland, hio,.assignors to The Cleveland Fuel. Equipment Company, Cleveland Ohio.

Application Iul'yf1`5, 19531', Serial-"'lo.V 368,154

Claims.. Cl. 2367-14).

Thisinvention relatestocontrolr devices and more particularly to an= adjustable means: incorporated intoa furnace control system tot regulate. the air thatv is carburetted with the fuel` t0:- produceI optimum conditions of combustion;

Control?` devicesusedvtoday in. both; domestic and industrial furnace;- installations; are: operable` to: introduce fuel: into the combustionl cham-ller wherein air. is combined. withthe` injected; fuel, and'. the: mixture: is then ignited producing; the heat necessaryf t'oz sustain the operation of the furnace.

The, air supplied: to thev combustion chamber. may be controlled by a wafer-type:valve; .comm'onlyl referred: to in the art as a-.damper,. whichgis` located ink the; furnace* stack system.

The damper is usually opened: j'ust; prior tot thea intro'- duction of the fuel tov the: combustion'. chamberg. and; as a result the draftI createdV is: often; excessive and;l the pilot flame isblownout. causingtthe-l furnace toishut` down` and continuously recycle: If. theA damper' isopened an insufficient amount, noty enough air is allowed. to'v enter the combustion chamber tor` enable proper: purging of the chamber and stack, and-iuporf firing. ofi the fuel any: gases that have not been so removedusuall-y resultin explosions that may be very detrimental to: the furnace or to operators.

Our device comprises anovel means whereby the damper is automatically adjusted to; a; safe. light-up positionresulting in; a correct predetermined: draft' for a subsequent igniting. of the.A fuel, and permitting proper purgingy of the unit. withoutv affecting: the.. pilot llame or existing lire bed, and which` thereafter modulates thev draft.

Further# advantages of our' invention; willv be realized by those familiar' in the art. and. a: morethorough understanding thereof. wille. result by." referring to: the'v accompanying drawing` which formsa part of this specification.

Fgl is a wiring diagram. shown partly. in diagrammatic form illustrating one embodiment of our invention' used in conjunction withv zu typical furna'ce-v electrical control system, and Fig.. 2` isa. plan View: showing' one: structural embodiment of the present invention.

Briefly, our invention: comprises. switch; means fV that are mounted on asliding; mechanism. and movable over the operatingl range of.' af. thrust arm member 8i The thrust arm 8- moves longitudinally with; respect; to the switch. mechanism, and; is adapted, tot trigger the switch means to control the damper for safe draft conditions;

The furnace construction per se,. in; which our' device is; incorporated may be. any oney of. the.: class of.; installation well known. in the4 art: comprisingl generally a boiler having a combustion. chamber,I a burner. extending into the. combustion chamber and adapted to burn` fuel. supplied from a` fuel reservoir; and a pilotfla-me or re. bed for igniting the` fuel. A staclc 251 connected tothe combustion chamber and has. adraft damper'9 for regulatingv the air entering` the stack'aud hence the.l air inthe furnace.

Briefly, in operation, the: damper control device; of'. the present invention opens. the. damper 9 toallowair to purge they combustion chamber4 and stack of any gasesthat are present as a result. of previous firing of. the boiler. The draft provided. by the opening, of. the,- damper is limited by said. device to. what. is. commonly known in the art as the safe light-up position, which position provides a thorough purging, of. thev furnace,y without.' affecting the pilot llame on gas or oilv installationslor exist.L ing fire bed on coal installations.

A draft indicator 16 whichzmay be. located. in. thet stack, determines when a. sufficient steadyf draft hasI been estabilished, and then. signals the'electrical controle. system-that it is safe to supply fuel. tothe combustion chamber. Fuel enters the. combustion. chamber via burners on oilY or gas furnaces, or via a Stoker unit to` aI tirez bedY ontcoal. burning installations. The pilot. llame orv existingv re ignites; the fuel' thereby commencingvk the burning" process..

When it has been definitely established thatthefuel is being consumed, a llame detector means 17- signals the electrical. control. system. to begin modulating.; the draft. A sample ofv prevailingpressure in thevcombustion chamber is transmitted. to the. electrical. control', system which determines whether there is. an excess or deficiency of. air. in the chamber.

A modulatingor balance switch meansdifferentiatesfthe pressure sample, and. is adaptedA to. connect electrical eniergy to the. damper control device 2. which opens or closes the damper 9 proportionalto the measured pressure; andthereby providesfor optimum conditions of combustion. When the. heating system. has reached its normal operating. pressure, a steam pressure. switclr 4 acts-to shut o. the fuel supply to the burners, and the electricalcontrol system operates to'readyV the system for the next cycle.

On installations using gas or oil as the combustible fuel the. electrical control system. and damper controll unit operate-to substantially` close the damper 9, while onthose units utilizing.' coal, the draft is continuously modulated until the next cycle.

More specifically, Fig. l illustrates one electrical control. system which may be used with thenovel damper control device of the presentinvention. The: switch', contacts and relay contacts, Fig. l, are shown.. in. their re;- spective open or closed position.A whichprevails during the standby condition, awaiting a demand for heat.. The circuitry to the left of. line A-A, Fig. l,` depicts a typical electrical controlV system, the particular conguration. of which may be modified for eachl furnace installation, and which is not a part of the presenti invention. The. circuitry to the right ofline' A-A depicts the, electrical configuration of the damper control device: adaptable'to thev particular illustrated electrical control. systenr of the furnace.

For automatic sequence control,.u.tilizing'the.illustrated circuit, the selector switch 3f isf placed into. the automatic position as shown in Fig. l. The control switch 43 isA also placed into thev automatic position.. When the'. steam pressure in the boiler falls. below a predetermined operating pressure, the pressure switch 4 closes andi the coil 41 of'relay A is energized through lines 80` and' 81. The contactAl of relay A is thenclosed, connecting the motor 6 to the electrical power source vialine 80, through the selector switch 3, line 82,y contact A1 of relay A, line 83, contact C1 of relay C, line 84,. control switch 43', line 85, contact 44.' of bottom adjustable switchV 14, line 86, contact 45 of outward limit switch. 24, and line 8T. Theground 54 provides the returnv path forsaidv electrical energy` as iswell knownv in the` art. The motor* is connected to a drive. screw 7', Fig; 2, upon which is threaded a thrust arm S which is moved longitudinally when the motor is. energized, rectilinearlyY with` respect to motor 6.

The arm 8 is connected by chain or cable means 32 to the draft damper 9 to open said damper.

An adjustable switch assembly 10 comprising a top and a bottom switch 14 and 31, respectively, mounted juxtaposed to each other on a base 11 which is slidably mounted on an elongated base member 15, is adapted to be positioned on said base anywhere within the path of travel of the thrust arm 8. The position of said assembly depends upon the specific characteristics of each furnace installation and is customarily known in the art as the safe-light-up position.

An arm 12 having outwardly extending ngers 13, one

being slightly longer than the other, is adapted to slidably engage and operate the adjustable switch mechanism to stop the movement of the thrust arm 8. By making one finger longer than the other, it is possible for the system to be connected so that either the outward or inward movement of the thrust arm will open or close the damper a predetermined amount. We will assume for the sequential operation that the upper adjustable switch 14 on the switch assembly 10 is operated, utilizing the longer of the two fingers, and that the outward thrust of the arm S opens the damper.

The motor upon being energized, as described hereinabove, moves the thrust arm 8 outward until the upper switch 14 is triggered by the longer of the two fingers 13 of the lever arm 12, opening contact 44, Fig. l, whereby the motor circuit is opened stopping the longitudinal movement of the thrust arm. The function of the switch assembly is twofold; it disconnects the motor 6 from the electrical power source, and at the same time it connects the electrical power source to other elements of the control unit for subsequent operation.

When switch 14 is operated by the outward movement of the thrust arm, opening contact 44, the contact 46 of said switch 14 is closed, and energy is fed to contact 47 0f the time relay via line 85, contact 46, now closed, line 88, contact 48 of the lower adjustable switch 31, and line 89.

When relay A is first energized upon the closing of pressure switch 4 current is fed to the contact 49 of the draft indicator 16, which is usually positioned in the stack, via line 80, selector switch 3 and line 33.

The draft indicator 16 is of the type commonly known in the art, comprising a wafer or arm that is movable by the air draft in the stack and is operable to open or close a contact 49 carried thereby to make or break a circuit connected thereto. lf the draft condition in the stack is insuicient for safe lighting of the fuel, the contact 49 of the draft indicator is closed, and the time delay relay coil 51 is energized. The Contact 47 of the time delay relay is opened by the energization of coil 51 thereby preventing any energization of relay B. This circuit condition will prevail until a satisfactory steady draft is maintained, whereby the contact 49 will be opened, allowing contact 47 to be closed after a predetermined delay. The time delay relay may be of the well known clock type whereby a delay period is mechanically incorporated after the electrical energy is removed, after which the contact 47 is allowed to close.

During the period when a sufficient draft is being established, the damper being partially opened, the gases are removed from the stack and fire box.

It was previously mentioned that the outwardly extending fingers 13 of the lever arm 12 were of different length; the reason being, that if on the energization of the motor 6, the arrn 8 continues its rectilinear travel after operating the upper adjustable switch 14, the shorter finger will operate the lower adjustable switch 31 which reverses the motor 6 and brings the arm 8 back to the desired position. It is therefore realized that once the safe light-up position is determined, the arm 8 will always open the damper 9 to this position on its initial stroke.

After the predetermined delay period, the contact 47 of the time delay relay closes, and electrical energy is fed 4 to the coil 52 of the relay B via line 85, contact 46, line 8S, contact 48, line 89, contact 47, and line 50. Upon energizing relay B, the contact B1 of the relay B is closed, locking said relay in the circuit as long as sufficient draft conditions prevail.

A second (N. O.) contact B2 of this relay B is also closed allowing current to ow through line 80, pressure switch 4, line 81 and line 94 to a fuel feed motor which supplies the fuel to the burners.

The pilot iiame or existing fire bed ignites the fuel, and the tiame detector device 17, of which many various types are well known in the art, the particular device incorporated in the present system comprising a photo electric cell 55 and connected relay 55A having a coil 56 and contact 57, senses a burning of the fuel. The photo-electric cell 55 thereof receives a sufficient intensity of light from the ignited fuel, proving that the fuel has been ignited, and current then ows through said photo cell, and the coil 56 of the ame detector device 17 is energized closing the contact 57 of this relay and connecting the coil 58 of relay C to the electrical power source through line 80, contact 57 and line 93, whereby said coil 58 is energized.

When the coil of relay C is energized the contact C2 of this relay is closed, connecting the electrical power source to a balance switch 1 which modulates the amount of air that is required for optimum fuel combustion.

The balance switch 1 comprises a movable contact 61 connected to a diaphragm 19, Fig. l, which is connected to the power source through line 83, contact C2 of relay C, and line 99. Two stationary contacts 62 are connected to the outward and inward limit switches 24 and 23 respectively, and then to opposite ends of the winding of the motor 6. The upper stationary contact 62 is connected via line 86, contact 45 and line 87, and the lower contact 62 is connected via line 91, contact 63 and line 92.

The balance switch is adapted to energize the motor winding in either of two directions to provide reversible energization of the motor. A pressure sample of air taken from the combustion chamber of the boiler through the capillary tube 21, Fig. 1, controls the movement and switching action of the diaphragm 19 and contact 61. In the present circuit, wherein the outward thrust of arm 8 opens the damper, if the air pressure in the combustion chamber is found to be high the diaphragm 19 moves toward the upper stationary contact 62, and when the stationary and movable contacts 62 and 61 respectively, engage, power is transmitted to the motor 6 via line S6, contact 45 of the outward limit switch 24 and line 87 to move the thrust arm outward to open the damper to a greater degree. If the air pressure is found to be low, the diaphragm moves toward the lower contact 62 and when said stationary and movable contacts engage, power is transmitted to the motor 6 via line 91, contact 63 of the inward limit switch 23 and line 92, and the motor then rotates inthe opposite direction to move the thrust arm inward to close the damper.

The balance switch, by interpreting the pressure conditions within the tire box, is able to accurately regulate the opening and closing of the damper to give optimum fuel consumption and therefore maximum heat transfer within the operational limits of the thrust arm 8.

After the igniting of the fuel has been established, the damper control unit is adapted to cause the thrust arm 3 to travel between its outer limits defined by the inward and outward limit switches 23 and 24 respectively to provide the draft of air required. A finger 26 extends downwardly from lever 12 and is adapted to be in slidable engagement with said switches to disconnect the motor 6 from the electrical power source.

On oil or gas furnace installations, the modulated damping will continue until the system reaches its operative steam pressure, whereupon the steam pressure switch 4 is opened, and relay A is de-energized, stopping the fuel feed. When relay A drops out, the contact A2 of this relay closes, thereby connecting the motor 6 directly to the electrical power source through wire 80, selector switch 3, wire 82, contact A2 now closed of relay A, wire 72, control switch 43 (in auto position), line 91, contact 63 of inward limit switch 23, and line 92, thereby enabling the thrust arm 8 to completely close the draft damper 9. When the damper is closed, the lever 12 acting through finger 26 actuates contact 63 of the inward limit switch 23 to disconnect the electrical power source from the damper control unit and the electrical control system is then ready for the next cycle.

If the previous ring cycle was performed manually and the damper has been left fully opened, beyond the operating position of the switch assembly 10, whereby the contact 45 of the outward limit switch 24 is opened, and the conta-ct 54 of said switch 24 is closed, it isnt necessary to purge the combustion chamber and stack of captured gases. With these conditions prevailing, electrical energy is supplied directly to contact 47 of the time delay relay, through contact 54, now closed, and wire 89. The fuel is then supplied to the combustion chamber upon ldraft conditions becoming stabilized, as hercinbefore described. However, under normal conditions, the damper is returned to its fully closed position, wherein the adjustable switch assembly is utilized.

In installation wherein the inward thrust of the arm 3 opens the damper, contact 45 of the outward limit switch 24 is actuated by nger 26 to disconnect the electrical power applied to said damper control device 2.

On furnace installations using coal as the combustiblel fuel, modulated damping is continued at all times after the initial igniting of the fuel enabling optimum conditions of combustion to be realized.

If it is desired to operate the control unit manually, the control switch 43 is moved to the manual position as shown in Fig. l and the selector switch 2 may be manually manipulated to its open opposition or close position whereby electrical power is directed to the motor to open or close the damper. The damper driving unit 2 will operate to open or close the draft damper 9, or if desired, the unit can be disconnected from the electrical power source by moving the switch 3 to the off position as shown in Fig. l.

Having thus described our invention, we realize that extensive departures can be made therefrom without departing from the spirit or scope of our invention.

We claim:

1. In a furnace construction having a combustion chamber, electrically operable fuel feeding means and a burner system for the combustion chamber operable by an electrical control system connected to a source of electrical energy, a Stack damper for removal of by-products of combustion and to provide means for an air draft,

'means for regulating said stack damper comprising a movable member connected to said damper, motive means connected to said movable member, switch means interconnected between said motive means and said electrical control system and operable to dene the extreme limits of movement for said movable member and connected damper, switch means interconnected between said control system and said eXtreme limits switch means and operable to limit the initial opening of said damper, lrst circuit means in said electrical control system responsive to a demand for heat from said furnace to connect said fuel feeding means to said source of electrical energy to supply fuel to said combustion chamber, means connected to said fuel feeding circuit means and operable through said electrical control system and both said switch means to energize said motive means to initially open said damper, means attached to said movable member arranged to operate said switch means interconnected between said control system and extreme limits switch means to de-energize said motive means upon the initial opening of said damper to a position intermediate that determined by said extreme limits switch means, second circuit means in said electrical control system including means responsive to the combustion of said fuel and to the combustion chamber pressure and operable to connect said extreme limits switch means to said source of electrical energy whereby said motive means is energized to move said movable member within said extreme limits, said iii-st circuit means being arranged upon satisfying demand for heat to disconnect said combustion chamber pressure responsive means from said extreme limits switch means and to connect said electrical source of energy to said motive means through said extreme limits switch means to close said damper, and means on said movable member operable to engage said extreme limits switch means to disconnect said motive means from said electrical source of energy when said damper is fully close-d or fully opened.

2. The device as defined in claim l, and wherein the switch means interconnected between said control system and said extreme limits switch means are adjustably mounted to be positioned along a path parallel with respect to said movable member.

3. The device as defined in claim 1, and wherein the movable member comprises an arm member connected to the damper and in threaded engagement with the motive means, being rectilinearly movable relative to said motive means.

4. The device as deined in claim 1, and wherein an elongated finger is attached to said movable member and engages and operates said switch means interconnected between said control system and said eXtreme limits switch means upon movement of said movable member to limit the initial opening of said damper.

5. The device as defined in claim l, and wherein a pair of elongated fingers, one being shorter than the other, are attached to said movable member and engage and operate said switch means interconnected between said control system and said eXtreme limits switch means upon movement of said movable member to limit the initial opening `of said damper.

References Cited in the le of this patent UNITED STATES PATENTS 1,431,738 Shivers Oct. 10, 1922 1,696,601 Hall Dec. 25, 1928 2,155,642 Dewey Apr. 25, 1939 2,243,715 Miller May 27, 1941 2,253,170 Dunham Aug. 19, 1941 2,422,495 Morrow June 17, 1947 

